Recovery of oil from a reservoir usually results in simultaneous production of water with the oil. In many cases the oil and water are subject to mixing and shearing in subsurface pumps, and this results in the formation of water-in-oil or oil-external emulsions having a viscosity that is substantially higher than that of the original, “dry oil”. Because of wellbore hydraulics, the production of this oil-external emulsion, with its higher viscosity, increases lifting costs (larger pumps and more electrical power requirements) and often limits the production rate from the well, which reduces economic profitability. Often, demulsifier chemicals are added to the subterranean formation to either prevent emulsion formation or to break the oil-external, high viscosity emulsion. The added demulsifier chemicals are expensive specialty products and need to be customized to the oil, emulsion and reservoir characteristics in order for the desired performance to be achieved. What is needed is a simple, economic method for reducing the viscosity of the oil-water mixture.
Moreover, in some cases the original oil is so viscous, such as with some heavy oils, that even if no water is produced from the reservoir and no oil-external emulsion is formed, the production rate of the oil is nonetheless limited because of its high viscosity. Accordingly, a simple, economic method for reducing the effective viscosity of highly viscous oil is also needed.
A related problem in the production of oil is a need to obtain an increased flowrate of the oil through a pipeline, for example, a pipeline used to transport oil from the point of production to points of collection, transportation, or sale. The viscosity of the oil is a limiting factor in the efficient transportation of oil. As the viscosity of the oil increases, so do the related costs of transportation, such as pumping costs. Existing methods for increasing pipeline capacity are to heat the oil, dilute the oil with less-viscous hydrocarbon diluents, treat the oil with drag reducers, transport the oil in a core annular flow, or convert the oil into an oil-in-water (or water-external) emulsion having a viscosity lower than that of the dry oil. Methods for making water-external emulsions include adding expensive surfactants or adding surfactants simultaneously with raising the pH of the water-oil mixture by adding base such as sodium hydroxide or ammonium hydroxide. However, for many oils, these treatments do not result in emulsions that remain sufficiently stable for the long times needed to transport the oil to market. A need exists for an inexpensive method for making a water-external emulsion that remains stable for long periods of time, and can be easily and economically demulsified and separated into the constituent oil and water.